Casting and process of treating castings and the like



UNITED STATES FRED K. BEZZEN'BERGER AND.MALCOLM N. RICH, OF CLEVELAND, OHIO, ASSIGNORS TO THE ALUMINUM CASTIN'GS COMPANY, OF CLEVELAND,

OF OHIO.

OHIO, A. CORPORATION CASTING AND rnocrss or TREATING casrmes AM) THE LIKE No Drawing.

To all whom it may concern:

Be it known that we, FRED K. Bnzzniw- BERGER and MALCOLM N. RICH citizens of the United States, residing at (lleveland, in

the county of Cuyahoga and State of Ohio,

have invented certain new and useful Improvements in Casting and Processes of Treating Castings and the like, of which the following is a specification, reference being had therein to the accompanying drawing.

This invention relates to the treatment of metallic articles whereby pores or small openings therein are substantially stopped and the articles thereby rendered impervious to fluids. The treatment is applicable to all metallic articles which are porous, but is of special importance with castings of alloys of aluminum and other light metals which are subject to relatively great porosity and which should for many purposes be impenetrable by air, water, gasolene and other- One object of the invention is to provide.

Another object is to provide a method for the treatment of porous metallic articles by which a relatively. inert material is formed within the pores of such articles whereby the said pores are stopped-and thepassage of fluids through the'said articles prevented.

Another object is to devise a method or process for the treatment of porous metallic articles according to which anhydrous silica may be formed within the pores of the porous articles.

Another object is to provide a method of treatment for porous metallic articles by which a relatively inert or insoluble material is formed independently of the metals comprising the said articles.

Another object is to produce a metallic article, the pores of WlllCll are stopped with relatively inert or insoluble material.

Other objects will appear to those skilled in the art from the following description of the method and the preferred means of practising it.

Our process consists briefly in the formation, by chemical reactions within the pores of the articles, of solid precipitates practically insoluble in water or other common Specification of Letters Patent.

hour or more.

solvents. It is applicable to any metallic article which is relatively porous, because it is not dependent on the metal or metals compr1s1ng the article, provided however that the solutions which are employed, do not react 'harmfully on the articles to be treated. Since the process is especially valuable in the treatment of aluminum alloy castings, the method will for purposes of illustration, be described as carried out with such castings.

In the casting of aluminum alloys, especially in sand molds, difficulty has been experienced in making the castings suflicientl non-porous to prevent passage therethroug of such fluids as air, water, gasolene, etc. These fluids, in fact, are commonly used to test the porosity of aluminum alloy castings,

some fluids frequently being applied under a pressure of several pounds per square inch, although ordinarily no pressure is applied.

According to the preferred method of practising our invention castings which have been found toleak when subjected to air, water, or other fluids, are treated as follows: The casting is first immersed in a bath of'concentrated sodium silicate for about ail hour, then the casting is removedand di ped for one or two minutes in a bath of ilute sulfuric acid. Following this dipping, the casting is rinsed with water and then heated at a temperature of 100 0. (212 for an lt-is obvious that a solution of any soluble silicate may be used but for purposes of Patented July 5, 1921. Application filed November 24, 1919. Serial No. 340,406. I

illustration, we have selected sodium silicate as being preferable. While baths of varying degrees of concentration may be employed, a concentrated bath of sodiumsilicate (40 Baum; 1.38 specific gravity) has given good results. Y

It has been found in practice that a concentrated solution tends to retard the process where the pores in the article being treated are relatively small, and that, on the other hand, dilute solutions do not always produce, in a single treatment, a stoppage of the pores. This is due to the fact that a concentrated solution of sodium silicate is rather viscous and does not readily enter small openings in the articles. being treated, while the dilute solutions do not contain sufficient sodium silicate to produce, after precipitation, a quantity of silica which will stop the pores.

To insure penetration of the solution into the many small openings in the casting, it is desirable to immerse the casting in the silicate solution, the duration of the immersion depending on the size and thickness of the casting, the sizes of the openings or pores therein and the degree of concentration of the silicate solution. If the casting is very porous the solution will readily enter the pores but if the openings are small, a longer soaking is necessary to insure penetration to all the interstices. The length of time the articles should be immersed may, therefore, vary widely under different conditions, the period of about an hour specified in our preferred method having been found to give satisfactory results with the common aluminum alloys constituting articles such as automobile engine crank case and smaller parts cast in sand molds.

Several different acids might be used and in varying strengths with good results but we prefer to use a mineral acid such as h drochloric acid, sulfuric acid or acidsodlum sulfate. Baths of hydrochloric or sulfuric acid which have been found suitable were made by mixing one part of concen trated commercial rade acid with six parts of water. A suita le bath of acid sodium sulfate may be made by adding ten parts by weight of the sulfate to 100 parts by weight of water.

The action of the acid bath is to cause a precipitation of hydrosilicic acid or hydrous silica within the pores or openings of the casting as well as on the surfaces thereof, according to the chemical reaction.

an hour at a temperature above the boiling point of water will give satisfactory results but they may be heated at a lower temperature for lon er periods if desired. The pores are thus su stantially stopped with the insoluble silica and leakage through the casting is prevented. Repeated treatments may be made if necessary, where, as in the case of the castings having relatively large pores, the pores are not completely closed with the first treatment.

The final step of applying heat to the treated articles might be dispensed with but we prefer not to omit it because the hydrous silica is more easily soluble than the anmethod of practising the invention, it is to be understood that the method is not limited.

to the exact steps described but is limited only by what is claimed in the appended clalms.

What we claim is:

1. The method of rendering porous metallic articles impervious to'fluids which comprises the formation of silica within the pores of the said article and the partial dehydration of the silica.

2. The method of rendering porous metallic articles impervious to fluids, which comprises, first c'ausing a solution of a silicate to enter the pores in the article; second, bringing an acid solution intocontact with the silicate solution within the said pores; and third, heating the said article.

3. The method of rendering porous metallic articles impervious to fluids which com-' prises immersing the article in a bath of sodium silicate; then dipping the article in a bath of mineral acid; washing the surface of the casting with water; and finally heating the article.

eL-The method of rendering porous metallic articles impervious to fluids such as air, water or gasolene, which consists in, first, immersing the article in a bath containing a soluble silicate; second, dipping the article in a bath containing an acid capable of reacting chemic'ally with the soluble silicate to precipitate hydrosilicic acid; third, rinsing excess materials from the surfaces of the article; and fourth, heating the article to convert a part of thehydrosilicic acid into anhydrous silica.

5. The method of rendering porous metallic articles impervious to fluids such as air, water or gasolene which consists in, first immersing the article in a bath containing sodium silicate until the solution has penetrated the pores of the said article; second, dipping the article in a bath containing sulfuric acid whereby hydrosilicic acid is precipitated within the pores of the article; third, washing excess materials from the third, washing excess materials from the surfaces of the article, and fourth, heating the within the pores of the article is converted into anhydrous silica.

6. The method of stopping the pores of aluminum alloy castings whlgh consists in immersing the casting in a fluid reagent and causing the latter to penetrate the pores of the castlng, subsequently immersing the casting in another fluid reagent which enters the pores and reacts with the first fluid contained therein to 'form a precipitate which stops the pores, and heating the casting to change the nature of the said precipitate.

7. As a new article of manufacture, a

metallic article the pores of which are 10 stopped with silica.

8. As a new article of manufacture, an aluminum alloy casting having its ores stopped with partially dehydrated sillca.

In testimony whereof- We hereunto aflix 15 our signatures FRED K. BEZZENBERGER. MALCOLM N. RICH. 

